The present invention relates to a motor.
Recently, it has been desired to reduce cogging torque and the physical size of a motor. In particular, various types of motors mounted in an automobile, for example, an EPS motor used in a power steering device has been desired to have its cogging torque and physical size reduced further.
Accordingly, to reduce the cogging torque and the physical size of a motor, attention has been paid to using a segment conductor (SC) coil as the coil for a stator. For example, a variety of types of brushless motors in which the coil are provided to the stator have been proposed as referenced in Japanese Patent No. 3303773.
The SC coil refers to a coil formed by inserting a U-shaped split conductor referred to as a segment into each slot in a stator core in an axial direction and interconnecting the distal ends of each adjacent pair of the segments in a post-process by welding or the like. If the SC coil is used, the number of slots in the stator core can be increased to reduce the cogging torque and also improve the occupancy ratio of the coil in the slot, thereby reducing the size per unit power output of the motor per power.
In the SC coil stator, the U-shaped segments are interconnected at their respective distal ends by welding or the like, so that, to prevent each adjacent pair of the welding portions from short-circuiting each other, the welding portions are slightly separated radially from each other to increase the distance between those welding portions. It increases the diameter of the stator by the corresponding amount, leading to a disadvantage in terms of the physical size of the motor to some extent.
As the EPS motor used in a power steering device, a motor in which a control circuit unit is mounted on the outer circumferential surface of a tubular frame incorporating the stator has been proposed to reduce the size of the system as a whole as referenced in, for example, Japanese Patent No. 3593102.
Therefore, even if the SC coil is simply turned over to the stator of a motor, the radial size of the motor stays large because of the control circuit unit mounted onto the outer circumferential surface of the tubular frame, so that the motor cannot be miniaturized.
Further, to supply power to the coil from the control circuit unit, it is necessary to insert leads extending from the control circuit unit into the tubular frame and connect one end of each lead to a receiving terminal of the coil in the tubular frame. Moreover, the other end of each lead needs to be connected to an output terminal of a circuit board mounted in the control circuit unit. Therefore, the motor still remains large both axially and radially.